A fact that the HMCZ method is superior in various points to a regular CZ method (a Czochralski method) is well known. An apparatus for use in implementation of this HMCZ method is obtained by improving an apparatus adopting the regular CZ method and has a configuration that a magnetic field application device for magnetic field application is coaxially arranged on the outside of a heater for heating a quartz crucible to face each other with the quartz crucible sandwiched therebetween.
FIG. 7 is a schematic view showing an example of a manufacturing apparatus used when implementing a silicon single crystal manufacturing method based on the conventional HMCZ method.
This manufacturing apparatus is constituted of a silicon single crystal pulling device 70 and a magnetic field application device 71 arranged on the outside of the pulling device 70. The pulling device 70 includes a hollow cylindrical chamber 80, and a crucible is arranged at a central part of this chamber 80. This crucible has a double structure, and it is constituted of a quartz inner holding container having a bottomed cylindrical shape (which will be simply referred to as a “quartz crucible 75a” hereinafter) and a graphite outer holding container that is adapted to hold the outer side of the quartz crucible 75a and likewise has a bottomed cylindrical shape (a “graphite crucible 75b”).
These crucibles are fixed to an upper end portion of a support shaft 76 to allow their rotation and upward and downward movements, and a resistance heating type heater 78 is substantially concentrically arranged on the outside of the crucible. Additionally, a heat insulating material 79 is concentrically arranged at an outer periphery of the heater 78. Further, a silicon raw material with a predetermined weight that has been put into the crucible is molten by the heater 78 to turn to a silicon raw material melt 72.
A pulling wire (or a pulling shaft, and both the members will be generically referred to as a “pulling member 77” hereinafter) that rotates on the same axis as the support shaft 76 in an opposite direction or the same direction at a predetermined rate is arranged on a central axis of the crucible filled with the silicon raw material melt 72, and a seed crystal 74 is held at a lower end of the pulling member 77.
In such a manufacturing apparatus, the silicon raw material is put into the quartz crucible, the silicon raw material is molten in an inert gas atmosphere under a reduced pressure by the heater 78 arranged around the crucible, then the seed crystal 74 held at the lower end of the pulling member 77 is immersed in a surface of the melt, and the pulling member 77 is pulled up while rotating the crucible and the pulling member 77, thereby growing a silicon single crystal 73 at a lower end surface of the seed crystal 74. Further, when growing the silicon single crystal 73, a horizontal magnetic field is applied to the silicon raw material melt 72 by the magnetic field application device 71 coaxially arranged to face the silicon raw material melt 72 to sandwich the quartz crucible 75a therebetween.
As described above, when pulling up a single crystal from the silicon raw material melt in the quartz crucible, according to the HMCZ method, since heat convection of the melt can be suppressed and a fluctuation in temperature near a melt liquid level (a solid-liquid interface temperature of the pulled single crystal) with time is reduced, it is possible to obtain advantages that generation of dislocation or a defect is suppressed and that the silicon single crystal having a uniform and low oxygen concentration can be easily acquired. Furthermore, since the generation of dislocation or a defect is suppressed, even a single crystal having a large diameter can be readily manufactured. Moreover, since the convection is suppressed, it is also possible to obtain an advantage that a crucible wall is hardly degraded.
In the single-crystal manufacturing apparatus adopting the conventional HMCZ method, the central axis of the coil is arranged to coincide with the melt surface in the quartz crucible, thereby suppressing the convection near the melt liquid level and forming the heat convection in a portion below positions near the melt liquid level. In this apparatus, heat transfer to a boundary layer between the single crystal that is being pulled up and the melt is enhanced, a temperature difference between the periphery of the crucible and the boundary layer can be reduced, the melt sufficiently agitated in the portion below the positions near the melt surface is supplied to the boundary layer, and hence it is possible to obtain advantages that the single crystal having uniform characteristics can be obtained as compared with an apparatus adopting the regular CZ method and that a crack in the crucible due to heat stress can be avoided.
Here, with an increase in diameter of a single crystal in recent years, there is a demand of a large silicon single crystal having a diameter of 300 mm or above. With this demand, a silicon raw material having a weight of 300 kg or above must be molten in a large quartz crucible having a diameter of 800 mm or above to grow a silicon single crystal. There has been suggested an HMCZ method for controlling convection of the melt in growth of the silicon single crystal from such a large volume of silicon raw material melt (see, e.g., Patent Document 1). Additionally, in regard to control over an interstitial oxygen concentration of a silicon single crystal grown based on an HMCZ method, an apparatus that a curvature radius of a magnetic field to be applied is specified (see, e.g., Patent Document 2) or a method for setting a relative position of a magnetic field application device and a crucible in the vertical direction (see, e.g., Patent Documents 3 and 4) is disclosed.
However, even if the above-described method or apparatus is utilized to grow the silicon single crystal, control over a diameter of the single crystal or an oxygen concentration in the single crystal in a growth direction is difficult, and the diameter or the oxygen concentration is fluctuated, whereby there occurs a problem that the silicon single crystal cannot be manufactured in conformity to a demanded quality standard and a yield ratio of the silicon single crystal is lowered. Further, there also arises a problem that quality of the manufactured single crystal greatly differs depending on each manufacturing apparatus.